1. Field of the Invention
This invention relates to a fuel supply device for an internal combustion engine, including a fuel injector for injecting pressurized liquid fuel.
2. Description of the Prior Art
A so-called multi-point fuel injection system for an internal combustion engine is known which comprises a plurality of fuel injectors each mounted in one of a plurality of branch pipes of an intake manifold respectively communicating with a plurality of cylinders of the engine. Due to the fact that this multi-point fuel injection system has a plurality of fuel injectors and means for controlling fuel injections effected by the plurality of fuel injectors is complex in construction, the problem has arisen that a fuel supply system including the fuel injection system is high in cost. To obviate this problem, proposals have been made to use what is generally referred to as a single-point fuel injection system which comprises a single fuel injector arranged upstream or downstream of a throttle valve mounted in an intake passage defined in a throttle body. However, the single-point fuel injection system having its fuel injector disposed downstream of the throttle valve suffers the disadvantage that because the fuel injector is directly influenced by variations in the negative or subatmospheric pressure in the intake manifold, means for effecting control of fuel injections by the single fuel injector becomes complex in construction, thereby causing an increase in cost of the fuel supply system.
A throttle body fuel injection system having a fuel injector arranged upstream of a throttle valve as disclosed in U.S. Pat. No. 4,130,095, for example, has another problem that, since the intake fluid flow through the intake passage upstream of the throttle valve at an idling operation of engine and at a high-load and low rotational speed of engine has a low speed, the liquid fuel injected from the fuel injector is not sufficiently atomized to change the liquid fuel into a mist of uniformly broken-down minuscule particles of fuel and uniform fuel-air mixtures are unobtainable.
It would be possible to reduce cost in producing the fuel supply system, if the pressure at which the liquid fuel is injected from the fuel injector is lowered. However, it would be impossible to obtain uniform fuel-air mixtures if the pressure at which the liquid fuel is injected is lowered, because this would make it impossible to obtain sufficient atomization of the liquid fuel to change the liquid fuel into a mist of uniformly broken-down minuscule particles of fuel.